1. Technical Field
This invention relates to direct access storage devices (DASD) and more particularly to a system and method for supporting user specification of physical file formats for files.
2. Description of the Related Art
A disk drive is a data storage device which utilizes at least one rotatable disk with a magnetic medium on a major surface of the disk. Data are represented on the medium as a series a physical transformations of portions of the magnetic medium. The physically transformed regions are arrayed as data tracks at defined locations.
In magnetic disk hard drive systems, a transducer used to read and write data to the disk forms a portion of a body called a slider. The slider flies just off the surface of a rotating disk. The slider is attached on its backside to a suspension system which in turn is connected to an actuator arm. The actuator arm is used to selectively position the head over a desired track or track location during a read or write operation. The slider itself may be moved radially inward or outward to change the track over which the slider is positioned. Movement of the slider between concentric data tracks takes time both for the movement and for damping motion of the slider at the end of a movement.
The term format embraces several aspects of arranging and interpreting items recorded on the storage media. For example, digital data may be recorded using one of several coding schemes. Coding is a type of logical format. Physical formats for data tracks relate to physical location and arrangement of data, e.g. in concentric and spiral tracks.
The use to which the digital data is put has consequences for the physical format chosen for storage. For example, image data of both the still or video type implies demand for large quantities of data storage space. For video it can further be anticipated that there will be large bandwidth demands due to real time reproduction requirements. For video data, the order in which data is recovered is also highly predictable. It is good design to arrange tracks of video data in such a way as to coordinate movement of the slider (or other transducer) with simultaneous readout of data. Spiral tracks work best for this. Using spiral tracks and storing data in the order for recovery along the spiral tracks allows the slider to be kept moving continuously inward or outward along the tracks during reading. No time is lost moving the slider between tracks or for stabilizing position of the slider after movement between tracks.
Text files and other similar coded material are typically smaller than still image and video files. Records formed from text files need not be contiguous, allowing maximum utilization of available space. Concentric tracks aid in locating all such portions of such records quickly during a read operation.